The present invention relates to a diagnosing apparatus and a method for diagnosing apparatuses of an exhaust gas purification system.
More particularly, the present invention relates to improvements in a diagnosing apparatus and a method for diagnosing apparatuses of an exhaust gas purification system which is operated to purify exhaust gas in accordance with output signals outputted from vacuum switches. The vacuum switches are connected to an intake manifold which is used for an engine with a carburator of a vehicle.
A first conventional diagnosing apparatus, which uses a high grade computer, can easily diagnose several apparatuses of the exhaust gas purification system, however, a second conventional diagnosing apparatus, which uses a low grade computer, cannot diagnose the several apparatuses of the exhaust gas purification system, because of the low capacity level of the low grade computer.
An engine with a carburator, which is mounted in a vehicle, usually uses the second type of conventional diagnosing apparatus, because the cost of the vehicle can be decreased. The engine with the carburator uses engine load sensors (e.g., vacuum switches) for generating signals to the second conventional diagnosing apparatus, and the second conventional diagnosing apparatus diagnoses the engine load sensors on the basis of the generated signals of the engine load sensors.
A similar conventional diagnosing apparatus is disclosed in Japanese Patent Laid Open No. 57-200665. The conventional apparatus diagnoses a pressure sensor for increasing fuel in an exceeding supply condition by a turbo charger in accordance with a relationship between output signals from the pressure sensor, a throttle valve opening sensor and/or an air flow sensor.
A similar conventional diagnosing apparatus is disclosed in Japanese Patent Laid-Open No. 58-30446. This apparatus diagnoses an O.sub.2 sensor, however the apparatus is prevented from diagnosing the O.sub.2 sensor when the atmospheric pressure is below a predetermined value.
The conventional diagnosing apparatus indicates the results of diagnoses (i.e., the diagnosis) by on-and-off lamps. When the conventional apparatus diagnoses one of apparatuses of the exhaust gas purification system as out of order or when the conventional apparatus detects an abnormal condition of a control apparatus of the exhaust gas purification system, one of the on-and-off lamps corresponding to said one of the apparatuses is turned on.
As mentioned above, the engine with the carburator uses the vacuum switch, and the second conventional diagnosing apparatus diagnoses normally on the basis of the output signal of the vacuum switch when the vehicle drives on a usual low ground (i.e., drives at a low altitude).
On the other hand, when the vehicle drives at a high altitude (i.e., on a high ground), the intake manifold pressure is decreased, even if the engine outputs the same output power, because the atmospheric pressure at a high altitude is lower than that at a low altitude.
Accordingly, at high altitudes, the vacuum switch or sensor generates the signal under different conditions than the conditions under which the vacuum switch generates the signal at low altitudes.
As a result, the second conventional diagnosing apparatus cannot normally diagnose the apparatus of the exhaust gas purification system, because the apparatus of the exhaust gas purification system is diagnosed on the basis of the vacuum switch. And, in a case of diagnosing the vacuum switch itself, also the second conventional diagnosing apparatus cannot normally diagnose the vacuum switch, because the second conventional diagnosing apparatus uses the predetermined relationship for diagnosing the vacuum switch. Namely, at high altitudes, the second conventional diagnosing apparatus might diagnose the apparatus of the exhaust gas purification system and the vacuum switch as out of order on the basis of the output signal even if the apparatus of the exhaust gas purification system and the vacuum switch are operating normally.
In order to prevent the second conventional diagnosing apparatus from incorrectly diagnosing the apparatus of the exhaust gas purification system and the vacuum switch or the engine load sensors, on the high ground, (i.e., at a high altitudes) the high grade detecting apparatuses may be used, but their costs are extremely high.